Process of roasting ores.



'UNITED STATES- FREDERICK LAIsT, or ANAooNiiA, Molvvriilvn.

'A PROCESS 0F ROASTING GRES.

Specification of Letters Patent.

Patented Oct. 20, 1914.

Application lred November 22, 1913. Serial No. 802,480.

being had to the accompanying drawings,

forming a part hereof.

My invention has relation to improvements in processes of roasting ores; and it consists in the novel features more fully set forth' in the specification and pointed out in the claims. 4

In the drawings, 'the figure is a combined elevation and middle vertical section of va furnace adapted to carry out my process, the section being taken through one of the fireboxes. p

The basic principle involved inthe present process is disclosed in my United States patent on roasting furnace, dated August 19, 1913, Number 1,070,490, said furnace being one of the forms designed for carrying out the process.

The invention relates toprocesses of treating ores, the particular treatment depending lon the character and composition of the ore (or other material).

The process is specially adapted for roasting copper sulid ores, and for roasting and chloridizing such ores when containing silver, and is eminently desirable for treating low grade ores to bring their metal constituents into a forni suitable for leaching and finalA recovery by precipitation or otherwise.

To the principle involved in the process, the saving of a large percentage of fuel is mainly due, one of the objects sought by my invention being to minimize the consumption of fuel employed for firing the charge to be treated. i

A further object of my invention is to avoid undue volatilization of metallic chlorids especially,A in the roasting and chloridizing of copper ores," this being a decided advantage of my process; and it results from the fact that the chloridation of the'hot roasted calcine is carried on vWithout the application thereto either of extraneous heat, or without dependence on heat of com# bustion within the mass, and under conditions where the reactions involving the chloridation are not affected by the cooling infiuences of the atmosphere.

To obtain a clear understanding of the improved process, it will be convenient to describe a form of furnace in which the in.

vention may be practised to advantage.-

The furnace shown and described in my patent aforesaid, altered in one or twominor details, is eminently adapted for carrying on my process, although it is not to Vbe considered as the only apparatus or furnace available for my purpose. However, inasmuch as the -furnaoe referred to has in practice been identified with the basic principle of my invention, it lwill be convenient to. describe my process in connection Withsaid furnace, only so much of the description of the latter being herein entered into, as will suffice to make intelligible the details of the process.

The invention may be describedin detail as follows Referring to the drawing, F, represents the furnace (extending partly above and partly belowthe floor-line L), and a, b, c, d, e, f, the several superposed hearths in whichthe material is treated (the present being a six-hearth multiple-hearth furnace), the material delivered from the'feed-hopper H dropping from the upper hearths successively through the several hearths until it is delivered into the discharge hopper C, the hearths being provided. with the central and marginal` openings or drop-holes 0, o, for the passage "of the material. Passing centrally through the hearths 1s the rotatable hollowrabble-shaft 1 from which radis ate the series of hollow rabble or stirrer arms 2 extending into the several hearths and carrying rakes 3, by which the material 1s successively fed from o-ne hearth to the hearth immediately beneath it, the shaft and arms being provided with air or water-circulating cooling pipes P,.P, as fully understood in the art. l

i The present is a direct-fired furnace being provided with two diametrlcally opposite fire-boxes B, burning coal (though coal-dust,`

oil, orga-s may be substituted), each fire-box having a shaking grate G, an ash launder A, and a checkerwork arch W, and discharging its gases and combustion products into the hearth c or hearth number three counting from the top. This hearth is considerably ginal drop holes o of the second hearth (Z2) l (always counting from the top) discharge the material onto the floor of the third hearth c. In hearth 0 Jthe roasting ore is moving away. from the circumference toward the center drop hole o. Thev ore is likewise moving away from the fire-boxes, this being an important feature of my invention for the following reason t-In any' direct-fired furnace used for roasting copper ore for. leaching purposes, it is very important to avoid overheating any of the ore since to do so causes a portion of the copper contents to become insoluble in the leaching solution, owing to the formation of ferrite copper. The temperature on the second Hoor -or hearth b is by measurement approximately 540' degrees Fahr. about two feet radially from the point where the ore drops onto the third floor (o). Before the formation of insoluble copper (ferrite copper) becomes serious a temperature of at least 1100 degrees Fahr. must be exceeded,

so that. the quantity of insoluble copper on this floor (b) is negligible and it makes no difference what the relative movement of the ore and flame thereover may be. On the third floor (c) however, .conditions are different. Here we have a temperature of 1280 degrees Fahr. about two feet from the furnace walls and about'midway between the drop-holes (from hearth b) and the gas discharge or fire-box openings o, the temperature being even higher closer to the said openings. The ore dropping from the second floor (b) has a temperature of about 500 degrees'Fahr.; and were it permitted to move toward this region or zone of high.

temperature, the tendency would be for portions of the ore to become overheated and rendered insoluble as above pointed out. This overheating will obviously be much reduced by having the comparatively cool ore entering said heated region or zone, moved continually toward a region of less heat or lower tempearture, that is to say, toward the center of the hearth. Accordingly, in a multiple-hearth furnace, roasting ore for leaching by direct firing, it is essential that the direct-fired hearth shall be one in which the ore is moved toward the center or away from the zone of high temperature prevailing at the point of discharge of the gases from the fire-box into the hearth. -In my present construction therefore, the firebox is allowed to discharge into the third hearth 0 in which the rakes move the ore from the circumferencev toward the center. It is also important, order to minimize the formation of insoluble or ferrite copper, and to prevent the destruction and deterioration of the rabble arms and rakes in this hearth (c) -that the openings Ofrom the fire boxes shall be immediately under the roof of the third hearth, and that this roof shall be so high above the rabble arms that the flame will clear the arms and play between the roof and said arms. It is for this reason that a clearanceof from ten to twelve inches is left between the upper surface of the rabble arms and the roof of the thirdA hearth, the rabble arms being thus brought out of range of the gases from the openings O.

It is statedin my patent aforesaid that there are generally speaking two types of roasts made use of for rendering soluble in dilute acids the copper contents of sulid ores, to-wit:-(1,) an oxidizing or sulfating roast, and (2,) a chloridizing roast.7 In this classification of thetypes of roasts the term oxidizing must be considered in its generic sense, because whether the metal is converted into CUO, or CuSOJ, it must be oxidized, that is to say, the CugS is iirst converted into CuO and SO2, any S03 which may form converting the CuO to CuSO, and vthevresult is a mixture of CuO and CUSO4, the sulfating process being likewise anv oxidizing one, speaking generically. Specifically however, these types may be considered as three distinct types, to-wit:- (a) the oxidizing roast pure and simple which contemplates the conversion of the metal to the oxid; (b) the sulfating roast which contemplates the formation of the sulfate of the metal; and (c) the chloridizing roast by which metallic oxids and sul fates (together with undecomposed sulfids, such as the sulid of silver where silver is present) are converted into the chloride of the metals.

My process contemplates `the practice 0f either the rst two types, or it may combine all three, dependingq on whether silver is absent or present in the ore. If no silver is present, the ore charge is subjected merely to anoxidizing and sulfating-roast; if silver is present then the charge is subjected to a combination of oxidizing, sulfating and chloridizing roasts. The ore is oxidized on the three upper hearths or loors a, c, Sulfated on the three lower Iloors d, e, f, or sulfated and chloridized on said lower floors depending on the composition of the Ore, the temperature of the charge being raised sufficiently high on the oxidizing Alioors to permit of a subsequent rapid sulfating, or combined sulfating and cl1loridizmaterial discharged from the upper or oxi- Y dizing hearths or floors, and which works down through said oors.

Assuming that the ore treated is a copper suld with more or less iron as an impurity, ,u

but carrying no silver, the product of the oxidizing roast 'from the hearths a, b, c, is mainly CuO, FeO, (very little sulfating taking place on these oors so that the amount of CuSO4, and FeSO4 need not be considered). On the three lower floors fl, e, f, any undecomposed sulfids will be -converted intosulffates, the SO2 in the resence of oxygen (air entering these oors through an opening E in the ywall of the bottom hearth f) being converted into S03 which, combining with CuO, converts the` latter into CuSO4, the iron (and alumina if any) being likewise sulfated. This sul-` fating roast however, is effected without any direct lire from without, (and without material dependence of theheat of oxidation of the sulfur still remaining in the charge while traversing the lower hearths) but depends for its consummation on the heat conserved in the calcines as they drop from the upper oxidizing (a, c) to the lower sulfating hearths (d, e, f), and

while traversing said )lower hearths.

Again, assuming that the ore treated is a copper sulid carrying silver, the product of the oxidizing roast from the hearths a, b, c, is probably a mixture of CuO, FeO, Ag, AgZS, with small quantities of CugS, CuSOU Ag()4 and FeSO. In this case there takes place on the lower hearths (fl, e, f) a sulfating rcactionsimilar .to that above described, and concurrently therewith a chlof ridizing reaction, common salt (Na-Cl) being added to chloridize t'he silver. The salt is fed to the fourth floor (d) in proper quantities, either through the doors D or by means of any suitable form of automatic feeder discharging the salt onto the hearth at a convenient point, and well understood in theyart. The temperature of the floor (d) in which the salt is introduced is any wherefrom 850 to 1000 degrees Fahrenheit, this being sufficient to permit the salt which is introduced cold) to react with the metalv constituents contained in the hot calcines, the reactions continuing throughout the several chloridizing hearths. The salt chloridizes all the silver present and that portion of the copper (CuSO4) which may have escaped conversion into oXid on the upper ioors, although it is quite probable that a small portion of the copper oXid will likewise be converted into chlorid, the chlorid of iron which is likewise formed being broken up into the oXid by the heat and oXygen present. The reactionsidentified with thechloridizing step of the process are probably as follows Any unconverted copper sulfate, and copper oXid is discharged from the furnace with the silver chlorid and copperchlorid, and with any iron oxid present in the chloridized charge. The final product or calcine is cooled in any suitable ore cooler known to the art, and is subsequently leached, the leaching solution employed being water containing from three to `fifteen per cent. by weight of sulfuric acid and from four to ifteen per cent. by weight of common salt, such solution readily dissolving the several components of the calcine referred to (the gangue and sand of course being insoluble). The dissolved metallic salts may be subsequently recovered by precipitation or by any other method known to the art.

In all chloridizing-roasting, a certain percentage of the copper (usually as chlorid) volatilizes; and while under my process this percentage is reduced to a minimum, yet provision is herein made to save and condense these copper fumes (and any chlorin and S03) by leading the furnace gases (from the' pipes 25, 26 or otherwise) to a suitable absorption tower or Cottrell electric .precipitation apparatus, or both (not shown), a corresponding quantity of -air be ing admitted to the chloridizing and sul.

fating hearths (d, e, f) through an opening E 1in the bottom hearth (f), the oxygen of the air so admitted facilitating the chloridizing (and sulfating) reaction in said hearths (rl, e, f) and the air current assisting in carrying olf any volatile chlorids. y

By my'process the orc is brought rapidly to a roasting temperature, the oxidizing roast eliminating a considerable proportion of the -sulfur in the form of SO2, small portions in this roast entering in combination with portions of the metallic bases forming sulfates. The bulk of the metal (copper, where copper is roasted) is however converted into the oxid. The roasted ore or hot calcine without loss of heat, and fully insulated from the cooling influences of the atlar to that of the contents of a tireless cooker, tha is to say, without accession' or application, of extraneous heat. It may be stated in passing that the feed to the furnace contains from 2.5 to 3 per cent. of sulfur and still contains about one per cent. of sulfur when it drops from the third (o) to the fourth (d) hearth or floor. The finished calcine (that is to say, the product as it leaves the chloridizing or 'sulfating hearths) contains about live-tenths of one per cent. of sulfur, of which `one-tenth of one per cent. isin the form of undecomposed sulids and four-tenths of one per cent. in the form of sulfates. Of the one per cent.

of sulfur'present inthe calcine as it drops 1 from the third to the fourth hearth about nine-tenths is in the form of undecomposed sulids, and one-tenth in the. form of sul-v fate's. It follows .therefore that the quantity of Y,sulfid decomposed oroxidized -in the chloridizing or sulfat-ing hearths is about eight-tenths of one per cent. That is to Say,

of the nine-tenths per cent. of sulfids drop# ping from the third to thefourth hearth,

three-tenths have been converted into sulfates, which three-tenthsadded to the onetenth dropping into the chloridizing or sulfating hearths, makes up the inal fourtenths of sulfates in the finished calcine. One-tenth of the ninetenths per cent. of sulid dropping from .the third to the fourth hearth remains undecomposed in the. finished calcine, thev sulfur of the remainingl five-tenths of the nine-tenths sulfid oxidizing or being converted into SO2 or 4SO3 fumes (which are abstracted with any Volatile copper chlorid fumes and drawn into the absorptio tower). The yheat of oxidation from this small quantity of sulfuris neg-lible as compared with the great-am^ount of heat developed in the oxidizing hearths, and with Von which dependence is placed to )bring about the necessary reaction between the saltl which the calcines are charged as they enter the chloridizing hearths, thisfheat being that and. the meta-l constituents 'of the calcines.

It will thus. be 'seen that' no v,attempt is made herein to relyon the-undecomposed 'suldf content of the ore for the generation of heat-(by oxidation) in fthe chloridizing or sulfating'hearthathe object sought being to Vdecompose to the extent indicated, the sulids lin the= oxidizing,` hearths, the sulfur in themain-piassin'g ofas SOT Any sulfates which are formed, (and a-'portion of*Pl the oxids (GuO) present) freely'. react.

vthe metal constituents with the salt (NaCl) added in the second stage of theprocess, .the nascent chlorin attacking' the metals and converting the ,same into Vchlorids, as per reactions given above. The decomposition of the sulfids in the oxidizing hearths (a, I), c) is brought about by the high temperature of the ire gases from the fire-boxes B, operating in' v conjunction with the hot air and gases discharged into said hearthsfrom the sulfating hearths d, e, f, (through the drop hole o between the hearths c and d), said air and gases passing over and between the particles of the ore in its travel through the several hearths, whereby the gases reach every portion of the ore. The decomposition `of the sulflds by the oxidizing roast leaves but a small percentage of undecomposed sulfidto contend with in the chloridizing and sulfating hearths (the `major portion in said hearths being probably silver sulid). Thus the sulfur element as a `fuel and heat generator is practically eliminated in the chloridizing hearths, dependence 'being placed substantially entirely on the heat conserved in the roasted calcines `discharged from the oxidizing hearths (a,' b, c), to effect the necessary reactionA between'the salt (added to the calcines in the chloridizing or sulfating hearths) and Practically no heat (a negligible quantity) is generated in the chloridizing or sulfating hearths (unless it be that due to the the combustion of sulfur; and no conserved heat is dissipated, because the walls of the furnace `are eliectively insulated. The result is a perfect chloridation with a minimum volatilization of copper chlorid.v The process is adapted for treatment of any grade of ore, but specially low grade ores where it is desirable 1to bring their metal content into a soluble form for precipitation or other form of recovery.

The process is not to be understood as restricted to the treatment of ores any other material` adapted to be roasted, calcin/ed, oxidized. and subsequentlysulfated or chloridized. being contemplated by the invention.

Itv may be stated in passing that 'the-atmosphere", the object sought being to make the insulation as complete as possible.

A Q'Features of furnace construction illusv trated'but not alluded to are fully described in my patent aforesaid, and there is no occaof the calcines.

the in-v ',sul'atedwalls of the lower section of the furnace while serving to conserve the heat `in the mass or calcine discharged from the chemical reactions above referred to) from sion to describe them in the present connection. v

The fuel employed in my process (in the fire-boxes B, B) being restricted in its application to the oxidizing hearths (a, b, c), it follows 4that less fuel is required than would be the case Were the bottom hearths (cl, e, f) also fired.. The process is therefore exceedinglyr economical of fuel. 1 The bottom hearths it Will be seen, serve both .as sulfating and chloridizing hearths; sulfating alone Where no salt is used, and sulfating and chloridizing Where salt enters into the reaction.

Having described my invention, what I claim is:- 1. In the treatment of ores and other material,'the process of subjecting a charge of the ore vvhile traversing a treatment chamber to the action of hot reaction-supporting gases, introducing said gases in a direction conforming to the general 'direction of movement of the ore in said chamber to pre: vent overheating of the charge, removing the resulting hot calcines from the inuence of the said gases completing the treatment of the calcines thus remoVedWithOut further application of heat, and conducting the gases from the final treatment, to the charge traversing the treatment chamber aforesaid.

2. In the treatment of ores and other ma-4 terial, the process of subjecting a charge of the ore While traversing a treatment chamber to the action of hot reaction-supporting gases, removing the resulting hot calcines from the influence of said gases, completing the treatment of the calcines thus removed Without further application of heat, and conducting the gases from the final treatment, to the charge traversing the treatment chamberaforesaid.v

3. In the treatment of ores and other material, the process of ysubjecting a charge of the ore While traversing a treatment chamber to the action of hot reaction-supporting gases, removing the hot calcines from the infiuence of said gases, conducting said calcines in a heat-insulated chambercompleting the treatment of the calcines in said heat-insulated chamber Without further application of heat, and conducting the gases from the final treatment, to the charge traversing the treatment chamber.

4. In the treatment of ores and other material, theprocess of subjecting the ore While traversing a treatment chamber to the di-y rect fire of furnace gases Within said chamber, moving said charge from a zone of high, to a region of comparatively loW temperature, While in contact With said gases,

- removing the hot calcines from said region of low temperature to a heat-insulated chamber, completing the reaction Within the mass, in said chamber Without further apu plication of Iheat, and conducting the hot gases of said reaction to the one in treatment chamber.

5. In ,the treatment o'f ores, the process of subjecting the ore While traversing a treatment chamber to the direct fire of furnace gases within said chamber, stirring said charge in the chamber and moving the same vfrom a zone of high, to a region of comparatively louT .temperature While in contact with said gases, removing the hot calcines from said region of low temperature to a heat-insulated chamber, mixing with the calcines a quantity of salt and stirring the mixture in said insulated chamber in thev presence of oxygen without further application of heat, and conducting the hot air and gases of the final reaction to the ore in the treatment chamber.

6. In the treatment of ores, the process of subjecting a charge of the ore traversing a series of intercommunicating treatment chambers to 'the action of hot reaction gases circulating through said chambers, and initially directed into the chamber last traversed by the ore, moving the ore in said last mentioned chamber from a zone of high, to a region Vof comparatively loW temperature While in contact with the gases, removing the calcines from the region of loW temperature and conducting the same to a -heat-insulated chamber, stirring the calcines in said chamber without further application of heat, to complete .the reaction, and conducting the gases of the completed reaction 1nto the chamber into Which the first hot reaction gases are initially directed.

7 In an oxidizing, sulfating, and chlorldizing of ores, the process of feeding the ore successively through a series of intercommunicating treatment chambers, directing hot reaction-gases into the last chamber of said series and causing the gases to circulate through the several chambers, movingthe charge immediately entered by the react-ion gases from a zone of high to a region of comparatively 10W temperature, removing,

the hotpcalcines from said region of loW temperature, feeding the same through a succession of heat-insulated treatment chambers in the presence of salt and oxygen, stirring the mixture While traversing said insulated chambers, whereby the reaction completes itself `without further application of heat, and conducting the gases from said heat insulated chambers to the charge traversing the iirst treatment chambers.

8. In the treatment of ores and other material, the process of subjecting a charge of the ore While traversing a treatment chamber to the action of hot reaction gases for oxidizing the charge, removing .the hot calcines from the influence of said gases,

conducting the same intoA a heat-insulated` chamber, stirring the calcines in said cham- In testimony whereof I afflx my signature,

ber in the presencle of oxygen, Wferlby the in presence of two Witnesses.

treatment is comp eted Without rt er application of heat, and conducting the hot air FREDERICK LAIST' 5 und gases of the nal reaction from said `Witnessesz heat-insulated chamber into the rst men- ALBERT E. WIGGIN,

toncd treatment chamber. WARREN JENNEY. 

